U.S. Pat. No. 4,459,402 discloses copolyesters of 20-80 mol % trans 4,4'-stilbenedicarboxylic acid, 80-20 mol % terephthalic acid and/or 80-20 mol % 2,6-naphthalene-dicarboxylic acid and 100 mol % 1,4-butanediol having exceptionally high tensile strength. U.S. Pat. No. 4,414,382 discloses polyesters based on 90-55 mol % 2,6-naphthalenedicarboxylic acid, 10-45 mol % trans 4,4'-stilbenedicarboxylic acid, and 100 mol % ethylene glycol. U.S. Pat. No. 4,526,822 discloses a polyester of terephthalic acid and ethylene glycol modified with 10-40 mol % trans 4,4'-stilbenedicarboxylic acid.
Japanese Kokai 72348/74 discloses blends of poly(1,4-butylene terephthalate) and a polyester having an aromatic dicarboxylic acid content that has at least mol % trans 4,4'-stilbenedicarboxylic acid.
Heretofore, copolyesters prepared from 1,4-butanediol, minor amounts of trans 4,4'-stilbene dicarboxylic acid and one other dicarboxylic acid have not been known, particularly when the other dicarboxylic acid is selected from terephthalic acid, and isophthalic acid.